SPACE PROVIDED. Research Summary: The major goal of this research proposal is to understand the logic that governs how neural circuits give rise to complex behaviors. I have chosen to focus on aggression, a nearly universal animal behavior that is important for survival and reproduction. The biogenic amine octopamine (OA), and its vertebrate counterpart noradrenalin, play important roles in aggression, as well as a variety of other social behaviors. However, the neural circuits on which these molecules act to regulate different social behaviors have not been well characterized. The aim of this proposal is to characterize the circuits that mediate the effects of OA on aggressive behavior in the genetically tractable organism Drosophila melanogaster. As an inroad to this problem, I will use genetic tools to alter neuronal activity of octopamine receptor-expressing neurons in vivo in order to answer the following questions: How does the activity of neurons expressing octopamine receptor 2 (Oa2) influence aggressive behaviors? What are the specific subpopulations of Oa2 neurons that are responsible for aggression and do different populations control various aspects of aggressive behavior? How do these Oa2 neuronal circuits function to mediate aggression and what are the neural pathways that they modulate? I will address these questions with the following specific aims: Aim 1- Loss-of-function and gain-of-function manipulations of octopamine receptor signaling. Aim 2 - Identification and characterization of octopamine receptor neuronal subsets. Aim 3 - Characterization of the projections of individual Oa2 neurons and their post-synaptic targets. Relevance to public health: In humans, aggression that is unchecked, persistent, or expressed out of context has profound negative impacts on society. Aberrant aggressive behavior is also associated with numerous prevalent psychiatric disorders such as depression, post-traumatic stress disorder and alcohol addiction. Investigating aggressive behavior in a genetically tractable model organism will increase our understanding of the basic neural-circuit mechanisms used by the nervous system to control complex behavioral states, such as aggression.